Watanabe, in Bull. Chem. Soc. Japan, 37, 1325 (1964), teaches the conversion of benzonitrile to benzamide with precipitated copper and Urushibara copper (U-Cu). The precipitated copper was prepared from a cupric chloride solution and zinc dust and was reacted with benzonitrile in water for 8 hours to give a 7% yield of benzamide. U-Cu-A was prepared by mixing zinc dust with a solution of cupric chloride and then leaching the resultant product with 13% acetic acid. The reaction of benzonitrile in water with U-Cu-A for 8 hours gave a 24% yield of benzamide with no recovery of benzonitrile.
Watanabe in the same reference shows the use of a mixture of NiO+CuO in unspecified proportions to convert benzonitrile to benzamide in the presence of ethanol under reflux conditions. In 10 hours he received a 5% yield of benzamide. Also, Watanabe states in column 1 on page 1325 that in the reaction of aliphatic nitriles, the yield of amides is lower and side reactions are more pronounced when compared to the reaction using aromatic nitriles. For such reactions, he apparently used only nickel catalysts, but the same drawbacks would be expected for copper catalysts.
Watanabe et al., in Bull. Chem. Soc. Japan, 39, 8 (1966) also show the use of a "copper chromium oxide" catalyst, "Cu-CrO.sub.2," to convert benzonitrile to benzamide. Although the preparation is not-disclosed, Watanabe's catalyst apparently was not prepared according to the present invention since benzonitrile in water reacted in the presence of the catalyst for 8 hours gave only a 20% yield of benzamide.
Copper-chromium oxides may be generally referred to as Adkins catalysts, so named after a pioneer in the field, Homer Adkins. The oxides may be prepared by a number of different procedures -- for example, by the decomposition of copper ammonium chromate, by the decomposition of copper ammonium chromium carbonates, by the decomposition of copper-chromium nitrates or by grinding or heating together copper oxide and chromium oxides. Although the products of these reactions are generally regarded to be composed of copper oxide and chromium oxide of the general formula CuCr.sub.2 O.sub.4, Stroupe, in J.A.C.S. 71, 569 (1949) indicates that the exact nature of such copper-chromium oxides is not known. Any preparation that produces copper oxide in combination with chromium oxide apparently is acceptable to prepare such Adkins catalysts, with the product formed by the decomposition of the copper ammonium chromate being one of the best since the product is very finely divided.
The copper ammonium chromate salts may be prepared by mixing aqueous solutions containing molar equivalent amounts of copper nitrate and ammonium chromate. The precipitate thus formed is recovered and when slightly heated decomposes spontaneously with the evolution of heat to form copper-chromium oxide. A barium, calcium or magnesium compound may also be added before precipitation as a stabilizer.
The preparation of various copper-chromium oxides is taught by Connor et al. in J.A.C.S 54, 1138, (1932), Young et al. in U.S. Pat. No. 2,575,403, Kirsch et al. in U.S. Pat. No. 2,964,579, Adkins et al. in J.A.C.S. 72, 2626 (1950) and Groger, Z. Anorg. Chem., 58, 412 (1908); 76, 30 (1912).
At the present time, the principal method of producing acrylamide on an industrial scale is the acid-catalyzed hydration of acrylonitrile. The great disadvantages of this acid process have been the accompanying sulfate pollution and large amount of sulfuric acid wasted. Some acrylamide plants recover the waste sulfuric acid in the form of ammonium sulfate, but others neutralize and dispose of the waste acid. The problem of disposal, the problem of pollution and the expense of the wasted sulfuric acid have created a search for a better method of preparing acrylamide which does not have the disadvantages of the acid process.